The present invention relates to cementing operations and, more particularly, in certain embodiments, to settable compositions comprising wollastonite and pumice and associated methods of use in cementing operations.
In cementing operations, such as well construction and remedial cementing, settable compositions are commonly utilized. As used herein, the term “settable composition” refers to a composition that hydraulically sets or otherwise develops compressive strength. Settable compositions may be used in primary cementing operations whereby pipe strings, such as casing and liners, are cemented in well bores. In a typical primary cementing operation, a settable composition may be pumped into an annulus between the walls of the well bore and the exterior surface of the pipe string disposed therein or between the pipe string and a larger conduit in the subterranean formation. The settable composition may set in the annular space, thereby forming an annular sheath of hardened, substantially impermeable material (e.g., a cement sheath) that may support and position the pipe string in the well bore and may bond the exterior surface of the pipe string to the well bore walls or to larger conduit. Among other things, the cement sheath surrounding the pipe string should function to prevent the migration of fluids in the annulus, as well as protecting the pipe string from corrosion. Settable compositions also may be used in remedial cementing methods, such as in the placement of plugs and in squeeze cementing for sealing voids in a pipe string, cement sheath, gravel pack, subterranean formation, and the like.
A particular challenge in cementing operations is the development of satisfactory mechanical properties in a settable composition within a reasonable time period after placement in the subterranean formation. During the life of a well, the subterranean cement sheath undergoes numerous strains and stresses as a result of temperature effects, pressure effects, and impact effects. The ability to withstand these strains and stresses is directly related to the mechanical properties of the settable composition after setting. The mechanical properties are often characterized using parameters such as compressive strength, tensile strength, Young's Modulus, Poisson's Ratio, elasticity, and the like. These properties may be modified by the inclusion of additives.
One type of settable composition that has been used comprises Portland cement as the cementitious component. Portland cement is one of the more common cementitious components used throughout the world and is usually produced by a process that comprises sintering a mixture of a predetermined composition and then grinding the resulting Portland cement clinker. While Portland cement has been used in well construction and remedial cementing for a number of years, drawbacks to Portland cement include the energy requirements to produce Portland cement. These energy requirements greatly increase the cost of creating Portland cement. Efforts to reduce the cost of settable compositions have come in the form of replacing Portland cement with other solid particulate components.